1. Field of the Invention
The present invention relates generally to distance measuring systems, and more specifically, to a method and system for measuring a distance between transceivers having a low or zero intermediate frequency.
2. Background of the Invention
A multitude of wireless communications systems are common use today. Mobile telephones, pagers and wireless-connected computing devices such as personal digital assistants (PDAs) and laptop computers provide portable communications at virtually any locality. As described in the above-incorporated patent applications, the above-listed portable devices as well as other communication systems may be enhanced to provide distance measurement capability within portable or stationary wireless devices.
In particular, BLUETOOTH devices provide a wireless network operating in the 2.4 Ghz Industrial Scientific and Medical band and be enhanced to provide a measurement of distance between connected devices without adding a separate infrastructure as is required with systems such as the Global Positioning System (GPS), thereby providing distance measurement with low incremental cost (BLUETOOTH is a trademark of Bluetooth SIG, Inc., which is an acronym for Bluetooth Special Interest Group—a consortium of wireless device manufacturers).
The techniques described in the above-incorporated patents introduce distance measurement capability within transceivers that are synchronized by a relatively high Intermediate Frequency (IF), but modern Radio Frequency (RF) Integrated circuit (IC) designs may use a very low IF frequency or a direct conversion scheme with no IF frequency at all. In a transceiver implemented using a low or zero IF frequency, synchronization of the devices involved in the distance measurement becomes impractical, and thus the known distance measuring schemes are thwarted by the lack of synchronization.
In particular, the half-duplex techniques described in the above-incorporated patent application “DISTANCE MEASUREMENT USING HALF-DUPLEX RF TECHNIQUES” are techniques that require synchronization of a pair of transceivers to retain phase coherency between reception and transmission intervals of a half-duplex signal. Without synchronization, a phase measurement cannot be made and therefore no distance measurement. In a direct conversion half-duplex system or a half-duplex low IF system where synchronization is impractical, implementation of the known distance measurement techniques is impossible.
Therefore, it would be desirable to provide a method and system for measuring distance within a low or zero IF transceiver loop, so that distance between wireless devices may be made without requiring additional infrastructure and without synchronization of local oscillators between wireless devices.